Polycrystalline ultra-hard constructions, such as polycrystalline diamond (PCD) materials and PCD elements formed therefrom, are well known in the art. Conventional PCD is formed by combining diamond grains with a suitable solvent catalyst material to form a mixture. The mixture is subjected to processing conditions of extremely high pressure-high temperature, where the solvent catalyst material promotes desired intercrystalline diamond-to-diamond bonding between the grains, thereby forming a PCD structure. The resulting PCD structure produces enhanced properties of wear resistance and hardness, making PCD materials extremely useful in aggressive wear and cutting applications where high levels of wear resistance and hardness are desired.
Solvent catalyst materials typically used for forming conventional PCD include metals selected from Group VIII of the Periodic table, with cobalt (Co) being the most common. Conventional PCD can comprise from 85 to 95% by volume diamond and a remaining amount of the solvent catalyst material. The solvent catalyst material is disposed within interstitial regions of the PCD microstructure that exist between the bonded together diamond grains or crystals.
A problem known to exist with such conventional PCD materials is thermal degradation due to differential thermal expansion characteristics between the interstitial solvent catalyst material and the bonded together diamond crystals. Such differential thermal expansion is known to occur at temperatures of about 400° C., causing ruptures to occur in the diamond-to-diamond bonding, and resulting in the formation of cracks and chips in the PCD structure.
Another problem known to exist with conventional PCD materials also relates to the presence of the solvent catalyst material in the interstitial regions and the adherence of the solvent catalyst to the diamond crystals that is known to cause another form of thermal degradation. Specifically, the solvent catalyst material is known to cause an undesired catalyzed phase transformation in diamond (converting it to carbon monoxide, carbon dioxide, or graphite) with increasing temperature, thereby limiting practical use of the PCD material to about 750° C.
Attempts at addressing such unwanted forms of thermal degradation in PCD are known in the art. Generally, these attempts have involved treating the PCD to remove the solvent catalyst material therefrom. PCD materials that have been treated in this manner are referred to as being thermally stable. Such thermally stable polycrystalline diamond materials have a material microstructure comprising a polycrystalline matrix phase of bonded together diamond crystals, and a remaining phase comprising a plurality of pores or voids interposed between the diamond crystals resulting from the removal of the solvent catalyst material.
Such thermally stable polycrystalline diamond material formed from PCD typically does not include a metallic substrate attached thereto, as any metal substrate is either removed from the PCD before treatment, or if not removed beforehand, falls away from the PCD body after treatment by the removal of the solvent metal catalyst at the interface previously joining the PCD body to the substrate.
A problem known to exist with using such thermally stable polycrystalline diamond materials in conjunction with known cutting and/or wear applications is the need to attach the thermally stable polycrystalline diamond material to a substrate to provide a construction suitable for attachment with a desired cutting or wear device. However, such thermally stable polycrystalline diamond materials typically have a poor wetability and have a coefficient of thermal expansion that is significantly different from that of conventional substrate materials, thereby making it very difficult to bond the thermally stable polycrystalline diamond material to such conventionally used substrates.
Attempts to form compact constructions have been made by brazing the thermally stable polycrystalline diamond body to a desired substrate. However, such compact constructions comprising the thermally stable polycrystalline diamond material brazed together with a substrate, e.g., cemented tungsten carbide, are known to be easily fractured along the braze joint, which fracture is believed to be caused by the formation of voids and residual thermal stresses in the braze joint during the process of brazing. Thus, compacts formed by brazing such thermally stable polycrystalline diamond material to a substrate are known to be vulnerable to fatigue and/or impact damage at the interface during operation. Accordingly, compacts formed in this manner typically have a reduced service life that is not desired in most cutting and/or wear applications.
An alternative approach for using such conventional thermally stable polycrystalline diamond materials as wear and/or cutting materials has been to avoid the use of a substrate and attach the thermally stable polycrystalline diamond to the intended cutting and/or wear device directly, i.e., without the use of a substrate. However, because such thermally stable polycrystalline diamond materials are devoid of either a metallic material or a metallic substrate, they cannot (e.g., when configured as a cutter for use in a subterranean drill bit) be attached to a drill bit by conventional brazing process. Thus, use of such thermally stable polycrystalline diamond materials in this particular application necessitates that the thermally stable polycrystalline diamond material itself be mounted to the drill bit by mechanical or interference fit during manufacturing of the drill bit, which is labor intensive, time consuming, and which does not provide a most secure method of attachment.
It is, therefore, desired that a thermally stable polycrystalline construction be provided in the form of a compact that includes a substrate, and that has properties of improved bond strength when compared to the above-noted conventional thermally stable polycrystalline diamond compact constructions. It is also desired that such thermally stable polycrystalline constructions be provided in a manner that display reduced residual thermal stress when compared to conventional thermally stable polycrystalline diamond compact constructions.